U.S. patent application number 11/938997 was filed with the patent office on 2008-10-23 for zoom lens and image pickup apparatus including the lens.
This patent application is currently assigned to CANON KABUSHIKI KAISHA. Invention is credited to Norihiro Nanba.
Application Number | 20080259454 11/938997 |
Document ID | / |
Family ID | 39554982 |
Filed Date | 2008-10-23 |
United States Patent
Application |
20080259454 |
Kind Code |
A1 |
Nanba; Norihiro |
October 23, 2008 |
ZOOM LENS AND IMAGE PICKUP APPARATUS INCLUDING THE LENS
Abstract
A zoom lens easily performs image stabilization with a compact
and light image-stabilizing lens unit, properly corrects an
aberration change during image stabilization, and achieves high
optical performance. The zoom lens includes a first positive lens
unit, a second negative lens unit, a third positive lens unit, a
fourth negative lens unit, and a fifth positive lens. These lens
units are arranged in order from an object side toward an image
side, and are moved during zooming. The fourth lens unit is formed
by one lens component, and is moved in a direction having a
component that is perpendicular to the optical axis for image
shifting. The Abbe number of a negative lens that forms the fourth
lens unit, the thickness of the fourth lens unit on the optical
axis, and the focal length of the entire zoom lens at the wide
angle end are set appropriately.
Inventors: |
Nanba; Norihiro;
(Utsunomiya-shi, JP) |
Correspondence
Address: |
CANON U.S.A. INC. INTELLECTUAL PROPERTY DIVISION
15975 ALTON PARKWAY
IRVINE
CA
92618-3731
US
|
Assignee: |
CANON KABUSHIKI KAISHA
Tokyo
JP
|
Family ID: |
39554982 |
Appl. No.: |
11/938997 |
Filed: |
November 13, 2007 |
Current U.S.
Class: |
359/557 ;
359/676 |
Current CPC
Class: |
G02B 15/145121 20190801;
G02B 27/646 20130101; G02B 15/173 20130101 |
Class at
Publication: |
359/557 ;
359/676 |
International
Class: |
G02B 27/64 20060101
G02B027/64; G02B 15/14 20060101 G02B015/14 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 16, 2006 |
JP |
2006-310480 |
Claims
1. A zoom lens comprising: a first lens unit having a positive
refractive power; a second lens unit having a negative refractive
power; a third lens unit having a positive refractive power; a
fourth lens unit having a negative refractive power; and a fifth
lens unit having a positive refractive power, wherein the first to
fifth lens units are arranged in order from an object side toward
an image side, wherein zooming is performed by moving some of the
five lens units so that a distance between the first lens unit and
the second lens unit is longer, a distance between the second lens
unit and the third lens unit is shorter, and a distance between the
fourth lens unit and the fifth lens unit is longer at a telephoto
end than at a wide angle end, wherein the fourth lens unit is
formed by one lens component, and is moved for image shifting in a
direction having a component that is perpendicular to the optical
axis, and wherein the lens component includes a negative lens, and
the following conditional expressions are satisfied: 63<.nu.4,
and D4/fw<0.3, where .nu.4 represents the Abbe number of the
material of the negative lens, D4 represents the thickness of the
fourth lens unit on the optical axis, and fw represents the focal
length of the entire zoom lens at the wide angle end.
2. The zoom lens according to claim 1, wherein the following
conditional expression is satisfied:
0.2<(R4a+R4b)/(R4a-R4b)<1.0 where R4a represents the radius
of curvature of a lens surface of the fourth lens unit closest to
the object side, and R4b represents the radius of curvature of a
lens surface of the fourth lens unit closest to the image side.
3. The zoom lens according to claim 1, wherein the following
conditional expressions are satisfied: 1.0<|f4|/fw<4.0, and
-1.2<(1-.beta.4).times..beta.5<-0.4, where f4 represents the
focal length of the fourth lens unit, and .beta.4 and .beta.5
respectively represent the lateral magnifications of the fourth
lens unit and the fifth lens unit.
4. The zoom lens according to claim 1, wherein the fourth lens unit
includes an aspherical surface, and the following conditional
expression is satisfied:
1.times.10.sup.-4<x/|f4|<1.times.10.sup.-2 where x represents
the maximum amount of displacement of the aspherical surface from a
reference spherical surface, and f4 represents the focal length of
the fourth lens unit.
5. The zoom lens according to claim 1, wherein the following
conditional expressions are satisfied: 3.0<f1/fw<6.0, and
0.9<|f2|/fw<1.4, where f1 represents the focal length of the
first lens unit, and f2 represents the focal length of the second
lens unit.
6. The zoom lens according to claim 1, wherein the following
conditional expressions are satisfied: 1.5<f3/fw<2.5, and
1.5<f5/fw<3.0, where f3 represents the focal length of the
third lens unit, and f5 represents the focal length of the fifth
lens unit.
7. The zoom lens according to claim 1, wherein a distance between
the third lens unit and the fourth lens unit at the wide angle end
is equal to that at the telephoto end.
8. The zoom lens according to claim 1, wherein the fourth lens unit
is formed by a biconcave negative lens.
9. The zoom lens according to claim 1, wherein the fourth lens unit
includes a biconcave negative lens and a resin layer provided on at
least one surface of the negative lens, and a surface of the resin
layer in contact with air is aspherical.
10. The zoom lens according to claim 1, wherein the zoom lens forms
an image on a solid-state image pickup element.
11. An image pickup apparatus comprising: the zoom lens according
to claim 1; and a solid-state image pickup element configured to
receive an image formed by the zoom lens.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a zoom lens and an image
pickup apparatus including the zoom lens that are suitably used in
electronic cameras, such as a video camera and a digital still
camera, a film camera, and a broadcasting camera.
[0003] 2. Description of the Related Art
[0004] A zoom lens for use in an image pickup apparatus, such as a
digital camera or a video camera, including a solid-state image
pickup element is required to have a compact optical system, a high
zoom ratio, and an image stabilizing function.
[0005] A positive lead zoom lens in which a lens unit closest to
the object side has a positive refractive power can easily achieve
a high zoom ratio, and therefore, is frequently used particularly
as a zoom lens having a zoom ratio of 10 or more.
[0006] As a positive lead zoom lens, a compact five-unit zoom lens
having a high zoom ratio is known in which five lens units having
positive, negative, positive, negative, and positive refractive
powers are arranged in that order from the object side to the image
side.
[0007] U.S. Pat. Nos. 5,388,004, 5,659,426, 5,771,123, and Japanese
Patent Laid-Open No. 2002-228931 disclose five-unit compact zoom
lenses in which a fourth lens unit having a negative refractive
power is formed by one component.
[0008] Further, zoom lenses having an image stabilizing function
are also known. In the zoom lenses, image blurring caused when
vibration is accidentally transmitted to an imaging system is
compensated by moving some of the lens units perpendicularly to the
optical axis.
[0009] A five-unit zoom lens disclosed in Japanese Patent Laid-Open
No. 2000-298235 has an image stabilizing function for correcting
image blurring by moving a third lens unit perpendicularly to the
optical axis.
[0010] Particularly when the image-stabilizing lens unit is moved
perpendicularly to the optical axis in the zoom lens, it is
required to have a small size and a light weight for the purpose of
size reduction and power saving of a moving mechanism.
[0011] Moreover, the zoom lens is required to have high optical
performance while suppressing changes in aberration during image
stabilization. In order to satisfy the above requirements, it is
important to properly set the zoom type and the lens configuration
of the image-stabilizing lens unit.
SUMMARY OF THE INVENTION
[0012] The present invention is directed to a zoom lens in which
image stabilization can be easily performed with a compact and
light image-stabilizing lens unit, a change in aberration during
image stabilization is properly corrected, and high optical
performance is achieved.
[0013] A zoom lens according to an aspect of the present invention
includes a first lens unit having a positive refractive power, a
second lens unit having a negative refractive power, a third lens
unit having a positive refractive power, a fourth lens unit having
a negative refractive power, and a fifth lens unit having a
positive refractive power. The first to fifth lens units are
arranged in order from an object side toward an image side. Zooming
is performed by moving some of the five lens units so that a
distance between the first lens unit and the second lens unit is
longer, a distance between the second lens unit and the third lens
unit is shorter, and a distance between the fourth lens unit and
the fifth lens unit is longer at a telephoto end than at a wide
angle end. The fourth lens unit is formed by one lens component. An
image is shifted by moving the fourth lens unit in a direction
having a component that is perpendicular to the optical axis.
[0014] The following conditional expressions are satisfied:
63<.nu.4, and
D4/fw<0.3,
where .nu.4 represents the Abbe number of the material of a
negative lens that forms the fourth lens unit, D4 represents the
thickness of the fourth lens unit on the optical axis, and fw
represents the focal length of the entire zoom lens at the wide
angle end.
[0015] Further features of the present invention will become
apparent from the following description of exemplary embodiments
with reference to the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a cross-sectional view of a zoom lens according to
a first exemplary embodiment of the present invention.
[0017] FIG. 2 includes aberration diagrams of the zoom lens at a
wide angle end in a first numerical example according to the first
exemplary embodiment.
[0018] FIG. 3 includes aberration diagrams of the zoom lens at an
intermediate zoom position in the first numerical example.
[0019] FIG. 4 includes aberration diagrams of the zoom lens at a
telephoto end in the first numerical example.
[0020] FIG. 5 is a cross-sectional view of a zoom lens according to
a second exemplary embodiment.
[0021] FIG. 6 includes aberration diagrams of the zoom lens at the
wide angle end in a second numerical example according to the
second exemplary embodiment.
[0022] FIG. 7 includes aberration diagrams of the zoom lens at the
intermediate zoom position in the second numerical example.
[0023] FIG. 8 includes aberration diagrams of the zoom lens at the
telephoto end in the second numerical example.
[0024] FIG. 9 is a cross-sectional view of a zoom lens according to
a third exemplary embodiment of the present invention.
[0025] FIG. 10 includes aberration diagrams of the zoom lens at the
wide angle end in a third numerical example according to the third
exemplary embodiment.
[0026] FIG. 11 includes aberration diagrams of the zoom lens at the
intermediate zoom position in the third numerical example.
[0027] FIG. 12 includes aberration diagrams of the zoom lens at the
telephoto end in the third numerical example.
[0028] FIG. 13 is a cross-sectional view of a zoom lens according
to a fourth exemplary embodiment of the present invention.
[0029] FIG. 14 includes aberration diagrams of the zoom lens at the
wide angle end in a fourth numerical example according to the
fourth exemplary embodiment.
[0030] FIG. 15 includes aberration diagrams of the zoom lens at the
intermediate zoom position in the fourth numerical example.
[0031] FIG. 16 includes aberration diagrams of the zoom lens at the
telephoto end in the fourth numerical example.
[0032] FIG. 17 is a schematic view showing the principal part of an
image pickup apparatus according to the present invention.
DESCRIPTION OF THE EXEMPLARY EMBODIMENTS
[0033] A zoom lens and an image pickup apparatus including the zoom
lens according to exemplary embodiments of the present invention
will be described below.
[0034] FIG. 1 includes cross-sectional views of a zoom lens
according to the first exemplary embodiment at a wide angle end
(short focal-length end), at an intermediate zoom position, and at
a telephoto end (long focal-length end). FIGS. 2, 3, and 4
respectively show longitudinal aberrations at the wide angle end,
the intermediate zoom position, and the telephoto end in the first
exemplary embodiment.
[0035] FIG. 5 includes cross-sectional views of a zoom lens
according to a second exemplary embodiment of the present invention
at the wide angle end, at the intermediate zoom position, and at
the telephoto end. FIGS. 6, 7, and 8 respectively show longitudinal
aberrations at the wide angle end, the intermediate zoom position,
and the telephoto end in the second exemplary embodiment.
[0036] FIG. 9 includes cross-sectional views of a zoom lens
according to a third exemplary embodiment of the present invention
at the wide angle end, at the intermediate zoom position, and at
the telephoto end. FIGS. 10, 11, and 12 respectively show
longitudinal aberrations at the wide angle end, the intermediate
zoom position, and the telephoto end in the third exemplary
embodiment.
[0037] FIG. 13 includes cross-sectional views of a zoom lens
according to a fourth exemplary embodiment of the present invention
at the wide angle end, at the intermediate zoom position, and at
the telephoto end. FIGS. 14, 15, and 16 respectively show
longitudinal aberrations at the wide angle end, the intermediate
zoom position, and the telephoto end in the fourth exemplary
embodiment.
[0038] FIG. 17 is a schematic view showing the principal part of a
video camera (image pickup apparatus) including the zoom lens
according to any of the exemplary embodiments of the present
invention.
[0039] In the lens cross-sectional views, the left side is an
object side (front) and the right side is an image side (rear).
[0040] The zoom lens according to each exemplary embodiment is an
imaging lens system used in the image pickup apparatus.
[0041] As shown in the lens cross-sectional views, the zoom lens
includes a first lens unit L1 having a positive refractive power, a
second lens unit L2 having a negative refractive power, a third
lens unit L3 having a positive refractive power, a fourth lens unit
L4 having a negative refractive power, and a fifth lens unit L5
having a positive refractive power. Herein, the refractive power
(optical power) is the reciprocal of the focal length.
[0042] The zoom lens also includes an aperture stop SP disposed in
the third lens unit L3 or near the third lens unit L3 (object side
or image side), and an optical block G corresponding to an optical
filter, a face plate, or the like.
[0043] When the zoom lens is used as an imaging optical system of a
video camera or a digital still camera, an image plane IP
corresponds to an image pickup surface of a solid-state image
pickup element (photoelectric transducer) such as a CCD sensor or a
CMOS sensor. When the zoom lens is used in a silver halide film
camera, the image plane IP corresponds to a photosensitive surface
such as a film surface.
[0044] In the aberration diagrams, d and g respectively represent a
d-line with a wavelength of about 587.56 nm and a g-line with a
wavelength of about 435.8 nm, and .DELTA.M and .DELTA.S
respectively represent a meridional image plane and a sagittal
image plane. Lateral chromatic aberration is represented by the
g-line. Fno represents the f-number, and .omega. represents the
half field angle.
[0045] In each of the following exemplary embodiments, the wide
angle end and the telephoto end refer to zoom positions provided
when the lens unit L2 for zooming is positioned at opposite ends of
a mechanical moving range in which the lens unit L2 is movable on
the optical axis.
[0046] In the zoom lens according to each exemplary embodiment, in
case of zooming from the wide angle end to the telephoto end, the
second, third, and fifth lens units L2, L3, and L5 are moved, as
shown by the arrows. Of course, the combination of the lens units
to be moved for zooming is not limited to the above, and some of
the five lens units can be moved to change the distances between
the lens units. For example, the first, third, and fifth lens
units, the second, third, fourth, and fifth lens units, the first,
second, third, and fifth lens units, the second and fourth lens
units, or all of the lenses can be moved.
[0047] More specifically, during zooming, the second lens unit L2
is moved to the image side, and the third lens unit L3 is moved to
the object side along a path including a convex portion.
[0048] The fifth lens unit L5 is moved to correct deflection of the
image plane due to zooming. This zooming method increases the zoom
ratio of the zoom lens.
[0049] A rear focus method in which focusing is performed by moving
the fifth lens unit L5 on the optical axis is adopted.
[0050] The fourth lens unit L4 is formed by one lens component
composed of a single lens or a cemented lens and having a negative
refractive power. The fourth lens unit L4 is moved in a direction
having a component that is perpendicular to the optical axis,
thereby changing the image forming position of the entire system
perpendicularly to the optical axis.
[0051] Since the fourth lens unit L4 having a negative refractive
power serves as an image stabilizing lens unit in this way, the
outer diameter of the lens is made smaller than when a lens unit
having a positive refractive power is used. This reduces the size
of the image stabilizing unit.
[0052] The aperture stop SP is disposed in the third lens unit L3,
or in front of or in the rear of the third lens unit L3. During
zooming, the aperture stop SP moves together with the third lens
unit L3. When the aperture stop SP is disposed in the third lens
unit L3, the distance between the second lens unit L2 and the third
lens unit L3 at the telephoto end is decreased. Therefore, the
overall length of the zoom lens can be shortened easily.
[0053] When the aperture stop SP is disposed on the object side of
the third lens unit L3, the distance between the aperture stop SP
and the first lens unit L1 is decreased. This is advantageous in
reduction of the diameter of the front lens system.
[0054] Each exemplary embodiment satisfies at least one of the
following conditional expressions:
63<.nu.4 (1)
D4/fw<0.3 (2)
0.2<(R4a+R4b)/(R4a-R4b)<1.0 (3)
1.0<|f4|/fw<4.0 (4)
-1.2<(1-.beta.4).times..beta.5<-0.4 (5)
1.times.10.sup.-4<x/|f4|<1.times.10.sup.-2 (6)
3.0<|f|/fw<6.0 (7)
0.9<|f2|/fw<1.4 (8)
1.5<f3/fw<2.5 (9)
1.5<f5/fw<3.0 (10)
where i represents the order number of the lens unit counted from
the object side to the image side, fi represents the focal length
of the i-th lens unit, fw represents the focal length of the entire
system at the wide angle end, .nu.4 represents the Abbe number of
the material of the negative lens that forms the fourth lens unit
L4, D4 represents the thickness of the fourth lens unit L4 on the
optical axis, R4a represents the radius of curvature of a lens
surface of the fourth lens unit L4 closest to the object side, R4b
represents the radius of curvature of a lens surface of the fourth
lens unit L4 closest to the image side, .beta.4 and .beta.5
respectively represent the lateral magnifications of the fourth
lens unit L4 and the fifth lens unit L5, and x represents the
maximum amount of displacement of an aspherical surface of the
fourth lens unit L4 from the reference spherical surface.
[0055] Advantages are achieved by satisfying the conditional
expressions. Technical meanings of the conditional expressions will
now be described.
[0056] Conditional Expression 1 defines the Abbe number of the
material of the negative lens that forms the fourth lens unit L4.
If the Abbe number is below the lower limit, dispersion becomes too
large, and chromatic aberration greatly varies during correction of
image blurring (image stabilization). Consequently, the chromatic
aberration is not corrected sufficiently.
[0057] Conditional Expression 2 defines the thickness of the fourth
lens unit L4 in the optical axis direction. If the thickness D is
above the upper limit, the effect obtained by forming the fourth
lens unit L4 by one component is lessened, and the size of the
image stabilizing unit is increased.
[0058] Conditional Expression 3 defines the shape factor of the
fourth lens unit L4. If the shape factor is less than the lower
limit and the curvature of the object-side surface is becomes too
small, an excessive spherical aberration occurs.
[0059] If the shape factor exceeds 1 as the upper limit in
Conditional Expression 3, the fourth lens unit L4 has a meniscus
shape with a concave surface pointing toward the image side. When
the degree of the meniscus is excessively high, the front principal
point of the fourth lens unit L4 is too close to the image side.
Therefore, it is difficult to ensure an air gap between the third
lens unit L3 and the fourth lens unit L4.
[0060] Conditional Expression 4 defines the focal length, that is,
the negative refractive power, of the fourth lens unit L4. When the
focal length is less than the lower limit and the negative
refractive power becomes too strong, if the number of lenses that
constitute the lens unit is small, the Petzval sum becomes too
small on the negative side, and a large field curvature occurs. In
contrast, when the focal length is more than the upper limit and
the negative refractive power becomes too weak, the radial size of
the fourth lens unit L4 is increased by a decrease in vibration
control sensitivity. Further, a light beam emitted from the fourth
lens unit L4 easily converges. Consequently, the focusing
sensitivity of the fifth lens unit L5 is lowered, and the amount of
movement of the fifth lens unit L5 during focusing is
increased.
[0061] Conditional Expression 5 relates to the vibration control
sensitivity of the fourth lens unit L4. In this expression,
(1-.beta.4).times..beta.5 represents the ratio of the amount of
shift of the component of the fourth lens unit L4 perpendicular to
the optical axis and the amount of shift of the image point on the
image plane. As this ratio increases, the amount by which the image
point can be shifted decreases.
[0062] When the vibration control sensitivity is below the lower
limit, the moving stroke (moving amount) for image stabilization
(image shift) increases, and the effective diameter of the fourth
lens unit L4 increases. This increases the size of the lens holder
and the image stabilizing mechanism.
[0063] In contrast, when the vibration control sensitivity is above
the upper limit, the fourth lens unit L4 is driven minutely during
image stabilization. In this case, it is difficult to precisely
control the driving of the fourth lens unit L4.
[0064] Conditional Expression 6 defines the maximum aspherical
amount of the negative lens of the fourth lens unit L4. The
aspherical shape of the negative lens is determined so that the
negative refractive power gradually decreases away from the optical
axis, thereby correcting eccentric coma aberration and tilting of
the image plane during image stabilization.
[0065] When the aspherical amount is too small below the lower
limit in Conditional Expression 6, aberration correction is not
sufficient during image stabilization, and the effect of the
aspherical surface is not obtained. In contrast, when the
aspherical amount is too large above the upper limit, eccentric
aberration is overcorrected.
[0066] Conditional Expression 7 defines the focal length, that is,
the refractive power, of the first lens unit L1. When the focal
length is less than the lower limit and the refractive power is too
strong, spherical aberration frequently occurs at the telephoto
end. In contrast, when the focal length is more than the upper
limit and the refractive power is too weak, it is difficult to set
the lateral magnification of the second lens unit L2 at 1.times. at
the intermediate zoom position. The moving amount of the fifth lens
unit L5 for correcting an image plane variation is limited by
setting the lateral magnification of the second lens unit L2 at
1.times. at the intermediate zoom position. However, when the focal
length exceeds the upper limit, the moving amount of the fifth lens
unit L5 increases.
[0067] Conditional Expression 8 defines the focal length, that is,
the refractive power, of the second lens unit L2. When the focal
length is less than the lower limit and the refractive power is too
strong, an aberration change caused in the second lens unit L2 by
zooming increases.
[0068] In particular, changes in spherical aberration, coma
aberration, and curvature of field increase. When the focal length
is more than the upper limit and the refractive power is too weak,
the moving amount of the second lens unit L2 for obtaining a
desired zoom ratio increases, the total length of the lens
increases, and the diameter of the front lens increases.
[0069] Conditional Expression 9 defines the focal length, that is,
the refractive power, of the third lens unit L3. When the focal
length is less than the lower limit and the refractive power is too
strong, the Petzval sum excessively increases in the positive
direction, and an under-correction of the curvature of field
occurs. In contrast, when the focal length is more than the upper
limit and the refractive power is too weak, the total length of the
lens increases.
[0070] Conditional Expression 10 defines the focal length, that is,
the refractive power, of the fifth lens unit L5. When the focal
length is less than the lower limit and the refractive power is too
strong, it is difficult to ensure a back focus having a length
necessary for insertion of a filter or the like. In contrast, when
the focal length is more than the upper limit and the refractive
power is too weak, the moving amount of the fifth lens unit L5 for
correction of an image plane variation due to zooming and for
focusing increases.
[0071] The numerical values in Conditional Expressions 1 to 10
should be set within the following ranges:
64<.nu.4 (1a)
D4/fw<0.2 (2a)
0.3<(R4a+R4b)/(R4a-R4b)<0.8 (3a)
1.5<|f4|/fw<3.5 (4a)
-1.1<(1-.beta.4).times..beta.5<-0.5 (5a)
1.2.times.10.sup.-4<x/|f4|<5.times.10.sup.-3 (6a)
4.0<f1/fw<5.4 (7a)
1.0<|f2|/fw<1.3 (8a)
1.6<f3/fw<2.2 (9a)
1.7<f5/fw<2.6 (10a)
[0072] Lens configurations of the lens units in each exemplary
embodiment will be described below.
[0073] The first lens unit L1 includes a cemented lens formed by a
negative lens and a positive lens, and a positive lens. The
cemented lens and the positive lens are arranged in that order from
the object side to the image side. This lens configuration allows
longitudinal chromatic aberration, lateral chromatic aberration,
and spherical aberration to be properly corrected while maintaining
a high zoom ratio.
[0074] The second lens unit L2 includes three lenses, that is, a
negative meniscus lens having a concave surface on the image side,
a negative biconcave lens, and a positive meniscus lens having a
convex surface on the object side, which lenses are arranged in
that order from the object side to the image side. The positive
lens is formed of a highly dispersive material so as to properly
correct a change in chromatic aberration resulting from
zooming.
[0075] The third lens unit L3 includes three lenses, that is, a
positive lens having a convex surface on the object side, a
negative meniscus lens having a concave surface on the image side,
and a positive biconvex lens, which lenses are arranged in that
order from the object side to the image side. By forming a space
between the positive lens on the object side and the negative
meniscus lens, the entire third lens unit L3 has a telephoto
structure, the distance between the principal points of the second
lens unit L2 and the third lens unit L3 is shortened, and the total
length of the zoom lens is shortened.
[0076] The fourth lens unit L4 is formed by one negative lens. In
the fourth exemplary embodiment, a resin layer having an aspherical
surface on the image side is added to the image side of the
negative lens. In each exemplary embodiment, the fourth lens unit
L4 is fixed during zooming. This can reduce a change in chromatic
aberration caused in the fourth lens unit L4 by zooming.
[0077] When the refractive power of the negative lens of the fourth
lens unit L4 is strengthened, spherical aberration occurs. This
spherical aberration is corrected by an air lens having a positive
refractive power and defined by the final lens surface of the third
lens unit L3 and an object-side lens surface of the fourth lens
unit L4. When the negative refractive power of the fourth lens unit
L4 is strengthened, pincushion distortion occurs at an image-side
lens surface of the lens unit. This pincushion distortion is
corrected by an air lens having a negative refractive power and
defined by the image-side lens surface of the fourth lens unit L4
and a lens surface of the fifth lens unit L5 closest to the image
side.
[0078] The fifth lens unit L5 is formed by a cemented lens having a
positive refractive power and constituted by a positive lens and a
negative lens. This configuration suppresses a change in chromatic
aberration resulting from correction of an image plane
variation.
[0079] In the exemplary embodiments, image blurring (displacement
of an image position) caused by vibration of the entire optical
system (zoom lens) is corrected by moving the fourth lens unit L4
in the direction having a component that is perpendicular to the
optical axis. This allows image stabilization to be performed
without adding an optical member, such as a variable-apex prism,
and a lens unit for image stabilization.
[0080] The fourth lens unit L4 is formed by one component so as to
reduce the size and weight of the image stabilizing unit. This
reduces the size and weight of the image stabilizing mechanism and
saves the power for driving the fourth lens unit L4.
[0081] In order to reduce changes in chromatic aberration during
image stabilization, it is necessary that chromatic aberration at
the fourth lens unit L4 should be sufficiently small. When the
fourth lens unit L4 is formed by one lens, it can be made of a
low-dispersion glass material in order to suppress chromatic
aberration. Further, in order to suppress eccentric coma aberration
and tilting of the image plane during image stabilization, it is
necessary that spherical aberration and coma aberration at the
fourth lens unit L4 should be sufficiently small.
[0082] These various aberrations are properly corrected with a
small number of lenses by appropriately setting the aspherical
surface in the fourth lens unit L4.
[0083] With the above structure, performance is enhanced by forming
the image stabilizing unit only by one lens component.
[0084] The fourth lens unit L4 can be formed by a replica
aspherical lens in which a thin resin layer having an aspherical
shape is provided on a spherical lens. In this case, the fourth
lens unit L4 can be manufactured more easily than when it is formed
as a glass-molded lens.
[0085] The refractive powers of the first lens unit L1 and the
second lens unit L2 are strengthened to some extent for the purpose
of size reduction of the optical system. This increases secondary
spectra of longitudinal chromatic aberration and lateral chromatic
aberration at the first lens unit L1 at the telephoto end.
[0086] Accordingly, these secondary spectra are properly corrected
by using a low-dispersion material, which has a high partial
dispersion ratio, for the positive lens that constitutes the
cemented lens of the first lens unit L1.
[0087] The aperture diameter of the aperture stop SP is changed
with zooming. The aperture diameter of the aperture stop SP is the
largest at the wide angle end, and decreases toward the
intermediate zoom position and the telephoto end.
[0088] This lowers the height at which off-axis rays pass through
the front lens from the intermediate zoom position to the telephoto
end, and thereby reduces the diameter of the front lens.
[0089] As described above, according to the exemplary embodiments,
the zoom lens includes five lens units, that is, a lens unit having
a positive refractive power, a lens unit having a negative
refractive power, a lens unit having a positive refractive power, a
lens unit having a negative refractive power, and a lens unit
having a positive refractive power. While the zoom lens provides a
high zoom ratio, the diameter of the front lens is small, and
aberrations can be properly corrected over the entire zoom range.
Moreover, the size of the zoom lens can be reduced, and aberrations
during image stabilization can be corrected properly.
[0090] An optical filter or a lens unit having a small refractive
power may be added to the object side of the first lens unit L1 or
the image side of the fifth lens unit L5.
[0091] Further, a teleconverter lens or a wide converter lens may
be placed on the object side or the image side.
[0092] An example of a video camera (image pickup apparatus) in
which the zoom lens according to any of the exemplary embodiments
of the present invention is used as an imaging optical system will
now be described with reference to FIG. 17.
[0093] Referring to FIG. 17, the video camera includes a video
camera body 10, an imaging optical system 11 formed by the zoom
lens according to the exemplary embodiment, an image pickup element
12, such as a CCD, which receives an object image from the imaging
optical system 11, a recording unit 13 that records the object
image received by the image pickup element 12, and a finder 14
through which the object image displayed on a display element (not
shown) is viewed. The display element is, for example, a liquid
crystal panel, and the object image formed on the image pickup
element 12 is displayed on the display element.
[0094] By thus applying the zoom lens of the exemplary embodiment
to the image pickup apparatus such as a video camera, the image
pickup apparatus can have a small size and high optical
performance.
[0095] The zoom lens according to the exemplary embodiments can
also be applied to a digital camera. The following first to fourth
numerical examples correspond to the above-described first to
fourth exemplary embodiments.
[0096] In the numerical examples, i represents the order number of
the lens surface from the object side, Ri represents the radius of
curvature of the lens surface, Di represents the lens thickness and
air gap between the i-th lens surface and the i+1-th lens surface,
and Ni and vi respectively represent the refractive index and the
Abbe number for the d-line. Two surfaces closest to the image side
are formed of filter members such as a crystal low-pass filter and
an infrared cut-off filter. B, C, D, and E are aspherical
coefficients. The aspherical shape given by the following
expression:
X = ( 1 / R ) H 2 1 + 1 - ( 1 + K ) ( H / R ) 2 + BH 4 + CH 6 + DH
8 + EH 10 ##EQU00001##
where X represents the displacement from the vertex of the surface
in the optical axis direction at the height H from the optical
axis, R represents the radius of curvature, and K is a conic
constant.
First Numerical Example
TABLE-US-00001 [0097] f = 6.69-64.60 Fno = 3.60-5.67 2.omega. =
53.2.degree.-5.9.degree. R1 = 33.964 D1 = 1.30 N1 = 1.805181 .nu.1
= 25.4 R2 = 21.459 D2 = 4.00 N2 = 1.496999 .nu.2 = 81.5 R3 =
-176.329 D3 = 0.10 N3 = 1.603112 .nu.3 = 60.6 R4 = 19.846 D4 = 2.40
N4 = 1.882997 .nu.4 = 40.8 R5 = 51.461 D5 = variable N5 = 1.696797
.nu.5 = 55.5 R6 = 41.993 D6 = 0.70 N6 = 1.922860 .nu.6 = 18.9 R7 =
5.801 D7 = 3.07 N7 = 1.693500 .nu.7 = 53.2 R8 = -26.431 D8 = 0.60
N8 = 1.846660 .nu.8 = 23.9 R9 = 20.477 D9 = 0.40 N9 = 1.603112
.nu.9 = 60.6 R10 = 11.001 D10 = 1.70 N10 = 1.487490 .nu.10 = 70.2
R11 = 28.281 D11 = variable N11 = 1.804000 .nu.11 = 46.6 R12 =
aperture stop D12 = -2.50 N12 = 1.846660 .nu.12 = 23.9 R13 = 10.496
D13 = 1.80 N13 = 1.516330 .nu.13 = 64.1 R14 = -35.835 D14 = 3.42
R15 = 49.037 D15 = 0.60 R16 = 8.281 D16 = 0.18 R17 = 12.002 D17 =
1.70 R18 = -18.402 D18 = variable R19 = -44.931 D19 = 0.70 R20 =
10.882 D20 = variable R21 = 14.255 D21 = 2.90 R22 = -13.213 D22 =
0.60 R23 = -52.741 D23 = variable R24 = .infin. D24 = 1.00 R25 =
.infin. Variable Focal Length Distance 6.69 34.34 64.60 D5 0.70
14.46 19.30 D11 21.60 5.33 3.00 D18 1.50 4.00 1.50 D20 7.06 2.53
9.15 D23 5.94 10.47 3.86 Aspherical Coefficient R14 k =
-1.57038e+02 B = -2.17502e-04 C = 2.02940e-05 D = -6.31367e-07 E =
0.00000e+00 R20 k = -2.33682e-01 B = -3.34645e-05 C = -2.74965e-06
D = 1.56954e-07 E = 0.00000e+00 R20 Effective Surface Diameter
.phi.7.0
Second Numerical Example
TABLE-US-00002 [0098] f = 6.57-64.60 Fno = 3.60-5.67 2.omega. =
54.0.degree.-5.9.degree. R1 = 33.377 D1 = 1.30 N1 = 1.805181 .nu.1
= 25.4 R2 = 21.174 D2 = 4.00 N2 = 1.496999 .nu.2 = 81.5 R3 =
-240.100 D3 = 0.10 N3 = 1.603112 .nu.3 = 60.6 R4 = 19.793 D4 = 2.40
N4 = 1.882997 .nu.4 = 40.8 R5 = 53.667 D5 = variable N5 = 1.696797
.nu.5 = 55.5 R6 = 44.810 D6 = 0.70 N6 = 1.922860 .nu.6 = 18.9 R7 =
5.910 D7 = 2.91 N7 = 1.693500 .nu.7 = 53.2 R8 = -31.654 D8 = 0.60
N8 = 1.846660 .nu.8 = 23.9 R9 = 18.575 D9 = 0.40 N9 = 1.603112
.nu.9 = 60.6 R10 = 10.881 D10 = 1.70 N10 = 1.516330 .nu.10 = 64.1
R11 = 28.343 D11 = variable N11 = 1.804000 .nu.11 = 46.6 R12 =
aperture stop D12 = 1.50 N12 = 1.846660 .nu.12 = 23.9 R13 = 10.638
D13 = 2.00 N13 = 1.516330 .nu.13 = 64.1 R14 = -38.183 D14 = 3.46
R15 = 57.052 D15 = 0.60 R16 = 8.362 D16 = 0.17 R17 = 11.582 D17 =
2.10 R18 = -22.242 D18 = variable R19 = -38.536 D19 = 0.50 R20 =
14.169 D20 = variable R21 = 14.777 D21 = 2.90 R22 = -17.837 D22 =
0.60 R23 = -69.384 D23 = variable R24 = .infin. D24 = 1.00 R25 =
.infin. Variable Focal Length Distance 6.57 32.31 64.60 D5 0.70
14.46 19.30 D11 20.08 3.81 1.48 D18 1.50 4.00 1.50 D20 6.07 2.63
9.28 D23 6.42 9.87 3.21 Aspherical Coefficient R14 k = -1.53867e+02
B = -1.73137e-04 C = 1.46800e-05 D = -3.82811e-07 E = 0.00000e+00
R20 k = -2.00596e-01 B = 7.52282e-07 C = -6.45104e-07 D =
1.81296e-08 E = 0.00000e+00 R20 Effective Surface Diameter
.phi.7.8
Third Numerical Example
TABLE-US-00003 [0099] f = 6.57-64.60 Fno = 3.61-5.67 2.omega. =
54.1.degree.-5.9.degree. R1 = 33.754 D1 = 1.30 N1 = 1.805181 .nu.1
= 25.4 R2 = 21.303 D2 = 4.00 N2 = 1.496999 .nu.2 = 81.5 R3 =
-213.917 D3 = 0.10 N3 = 1.603112 .nu.3 = 60.6 R4 = 19.936 D4 = 2.40
N4 = 1.882997 .nu.4 = 40.8 R5 = 53.974 D5 = variable N5 = 1.696797
.nu.5 = 55.5 R6 = 43.683 D6 = 0.70 N6 = 1.922860 .nu.6 = 18.9 R7 =
5.931 D7 = 2.91 N7 = 1.693500 .nu.7 = 53.2 R8 = -30.281 D8 = 0.60
N8 = 1.846660 .nu.8 = 23.9 R9 = 19.484 D9 = 0.40 N9 = 1.603112
.nu.9 = 60.6 R10 = 10.996 D10 = 1.70 N10 = 1.496999 .nu.10 = 81.5
R11 = 28.689 D11 = variable N11 = 1.804000 .nu.11 = 46.6 R12 =
aperture stop D12 = 1.50 N12 = 1.922860 .nu.12 = 18.9 R13 = 10.406
D13 = 2.00 N13 = 1.516330 .nu.13 = 64.1 R14 = -34.905 D14 = 3.21
R15 = 63.429 D15 = 0.60 R16 = 8.202 D16 = 0.18 R17 = 11.588 D17 =
2.10 R18 = -16.225 D18 = variable R19 = -26.281 D19 = 1.00 R20 =
10.539 D20 = variable R21 = 13.631 D21 = 2.90 R22 = -19.551 D22 =
0.60 R23 = -51.178 D23 = variable R24 = .infin. D24 = 1.00 R25 =
.infin. Variable Focal Length Distance 6.57 31.79 64.60 D5 0.70
14.46 19.30 D11 20.08 3.81 1.48 D18 1.50 4.00 1.50 D20 6.31 3.94
9.45 D23 5.88 8.26 2.74 Aspherical Coefficient R14 k = -1.28214e+02
B = -1.609166-04 C = 1.45672e-05 D = -3.28183e-07 E = 0.00000e+00
R20 k = -1.29868e+00 B = 4.10305e-05 C = 1.05034e-06 D =
-3.84822e-08 E = 0.00000e+00 R20 Effective Surface Diameter
.phi.7.6
Fourth Numerical Example
TABLE-US-00004 [0100] f = 6.60-64.60 Fno = 3.61-5.67 2.omega. =
53.8.degree.-5.9.degree. R1 = 32.924 D1 = 1.30 N1 = 1.805181 .nu.1
= 25.4 R2 = 21.055 D2 = 4.00 N2 = 1.496999 .nu.2 = 81.5 R3 =
-248.176 D3 = 0.10 N3 = 1.603112 .nu.3 = 60.6 R4 = 20.377 D4 = 2.40
N4 = 1.882997 .nu.4 = 40.8 R5 = 56.510 D5 = variable N5 = 1.696797
.nu.5 = 55.5 R6 = 43.312 D6 = 0.70 N6 = 1.922860 .nu.6 = 18.9 R7 =
5.928 D7 = 2.91 N7 = 1.693500 .nu.7 = 53.2 R8 = -30.329 D8 = 0.60
N8 = 1.846660 .nu.8 = 23.9 R9 = 19.619 D9 = 0.40 N9 = 1.603112
.nu.9 = 60.6 R10 = 10.895 D10 = 1.70 N10 = 1.496999 .nu.10 = 81.5
R11 = 27.754 D11 = variable N11 = 1.514210 .nu.11 = 51.4 R12 =
aperture stop D12 = 1.50 N12 = 1.804000 .nu.12 = 46.6 R13 = 10.298
D13 = 2.00 N13 = 1.922860 .nu.13 = 18.9 R14 = -33.400 D14 = 2.99
N14 = 1.516330 .nu.14 = 64.1 R15 = 61.357 D15 = 0.60 R16 = 8.105
D16 = 0.18 R17 = 11.585 D17 = 2.10 R18 = -13.897 D18 = variable R19
= -22.957 D19 = 1.00 R20 = 8.619 D20 = 0.10 R21 = 9.116 D21 =
variable R22 = 13.128 D22 = 2.90 R23 = -18.780 D23 = 0.60 R24 =
-51.178 D24 = variable R25 = .infin. D25 = 1.00 R26 = .infin.
Variable Focal Length Distance 6.60 31.90 64.60 D5 0.70 14.46 19.30
D11 20.08 3.81 1.48 D18 1.50 4.00 1.50 D20 6.73 4.97 9.69 D24 5.62
7.38 2.66 Aspherical Coefficient R14 k = -1.54303e+02 B =
-2.55352e-04 C = 2.38816e-05 D = -6.81134e-07 E = 0.00000e+00 R21 k
= -1.64957e+00 B = 8.28444e-05 C = 3.31601e-06 D = -1.15059e-07 E =
0.00000e+00 R21 Effective Surface Diameter .phi.6.4
[0101] In the fourth numerical example, the lens component defined
by the lens surfaces R19, R20, and R21 is a replica aspherical lens
in which a thin resin layer is provided on the lens surface R20 of
a spherical glass lens defined by the lens surfaces R19 and
R20.
[0102] Table 1 shows the relationships between the above-described
conditional expressions and the values in the numerical
examples:
TABLE-US-00005 TABLE 1 Numerical Example 1 2 3 4 Conditional 70.2
64.1 81.5 81.5 Expression 1 Conditional 0.10 0.08 0.15 0.17
Expression 2 Conditional 0.61 0.46 0.43 0.43 Expression 3
Conditional 2.66 3.04 2.28 1.97 Expression 4 Conditional -0.69
-0.62 -0.80 -0.92 Expression 5 Conditional 5.81 .times. 10.sup.-4
1.66 .times. 10.sup.-4 1.36 .times. 10.sup.-3 1.41 .times.
10.sup.-3 Expression 6 Conditional 4.84 4.98 4.95 4.94 Expression 7
Conditional 1.07 1.12 1.13 1.13 Expression 8 Conditional 1.85 2.03
1.87 1.77 Expression 9 Conditional 2.21 2.41 2.19 2.12 Expression
10
[0103] While the present invention has been described with
reference to exemplary embodiments, it is to be understood that the
invention is not limited to the disclosed exemplary embodiments.
The scope of the following claims is to be accorded the broadest
interpretation so as to encompass all modifications, equivalent
structures and functions.
[0104] This application claims the benefit of Japanese Application
No. 2006-310480 filed Nov. 16, 2006, which is hereby incorporated
by reference herein in its entirety.
* * * * *